This invention relates in general to systems for pressurizing tanks containing hydraulic fluid used to actuate hydraulic equipment and, in particular, to have a system for pressurizing the varying air space created in a tank containing hydraulic fluid used to operate auxiliary hydraulic actuators when quantities of hydraulic fluid are removed from and returned to the tank or reservoir.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a vehicle hydraulic fluid tank pressurization system actuated by and during operation of the hydraulic equipment independent of direct coupling to a source of air pressurized by the vehicle engine.
In the operation of vehicles having auxiliary hydraulic operated equipment operated by the selective coupling of a source of pressurized hydraulic fluid to the equipment, pressure fluctuations frequently occur in the fluid reservoirs of such systems during operation of the equipment. Such auxiliary equipment as hydraulic jacks frequently cause extensive changes in the volume of the hydraulic fluid retained in the tank due to the greater volume of fluid required when the jacks are extended than when retracted. These pressure variations frequently cause the hydraulic pump employed in these systems to draw the hydraulic fluid from the reservoir against a vacuum during periods of high fluid demand by the hydraulically operated equipment. This withdrawing of the hydraulic pump against a vacuum causes cavitation of the hydraulic fluid in the pump creating unnecessary and undesirable noise and an excessive amount of wear on various pump components.
In earth-moving vehicles or construction machines, due to the environmental conditions in which such equipment frequently operates, it is necessary that the hydraulic system be closed to prevent the hydraulic fluid from becoming contaminated by the dust, dirt, or other contaminants encountered by the vehicle during operation. Therefore, the source of pressurized air required to prevent pump cavitation must be filtered before being introduced into the hydraulic fluid tank.
In the past various methods have been utilized for maintaining a tank pressure at or slightly above atmospheric pressure. U.S. Pat. No. 3,130,548 discloses a system for pressurizing a hydraulic fluid tank which utilizes a single acting piston cylinder assembly which during extension of the piston rod pressurizes the hydraulic fluid tank. U.S. Pat. Nos. 3,039,823 and 3,846,983 disclose, respectively, systems for pressurizing the air space within a hydraulic fluid containing tank by means of pressurized air either from a compressor driven directly from the vehicle engine or from the engine turbo charger coupled in fluid communication with the hydraulic sump.
As is well known to those skilled in the art, if pressure within the air space is permitted to accumulate or increase to an excessive amount, it is possible that the sump tank will burst. Therefore, it is necessary to not only pressurize the sump tank, but to provide suitable pressure relief means to relieve excessive pressure in the fluid space. In all these prior art systems, the sump tank for containing the hydraulic fluid is equipped with a relief valve to release pressurized air from the air space when the pressure exceeds a predetermined maximum.
The present invention can be utilized to pressurize the air space within the hydraulic fluid tank on a vehicle which does not have a forced air intake and may be utilized without direct coupling to the engine air supply. In addition, the present invention does not require a pressure relief valve to be installed in the hydraulic fluid reservoir or tank but controls delivery of the pressurized air in response to the tank air pressure.